Method and apparatus for controlling the crop shear of a hot strip mill



ATTOR N EY J. W. COOK METHOD AND APPARATUS FOR CONTROLLING THE Nov. 10, 1970 CROP SHEAR OF A HOT STRIP MILL Filed Jan. 16, 1968 Tmm w R O o m C N E W W W n 56.50 I wz; z m 55500 8 J lll mop/52mm 55:8 SE28 3 5m J 6 5". A 1.65 n 2 llll mokomkmo w w w A owmmw x5228 5 g 5.33m flmwnw 51E 525 56% 65 20 o w 8 wk .12850 Swim 5 N2 :2 mv Q @9850 w 29:81

O MW. PP I |1|| III |||o on||so 0 110 ollldo lllo a 2 Q Q Q i United States Patent O 3,538,726 METHOD AND APPARATUS FOR CONTROLLING THE CROP SHEAR OF A HOT STRIP MILL John W. Cook, Williamsville, N.Y., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., 21 corporation of Pennsylvania Filed Jan. 16, 1968, Ser. No. 698,183 Int. Cl. B21!) 1/00 U.S. Cl. 727 6 Claims ABSTRACT OF THE DISCLOSURE This invention relates to the method and control system for operating a steel mill and proposes in particular to operate a crop shear normally used in the finishing mill to remove the rough ends of the strip, to cut a strip derived from a single slab to provide multiple coils.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to systems and methods for the reduction rolling of metal or other materials, and more particularly to the control operation of the crop shear to cut the strip into desired lengths.

Description of the prior art It has been the practice in hot strip mills to supply a crop shear on the entry side of the finishing mill to crop the head and tail ends of the strip before it enters the finishing mill. Typically, slabs of a material such as steel are first heated and then runthrough a roughing mill where the thickness of the slab is reduced successively by a series of stands. After repeated reductions of the thickness the head end of the strip becomes rounded to the degree that it becomes difficult to thread into the finish mill. The tail end of the strip is elongated by repeated reductions to form projections from the strip which may break off in the finishing mill. The broken pieces from the strip may cause damage not only to the succeeding strips to be processed but also to the mill itself. Therefore, the crop shear is normally used in a hot strip mill to remove the ragged ends of the strip to insure proper entry of'the head end and to minimize roll damage and strip breakage as the tail end of the strip passes through the mill.

The efficiency of operation of the newer and larger hot strip mills depends upon using extremely large slabs. Large slabs improve the heating efficiencies of the furnaces and minimize the slab handling problems to a great extent. However, in many instances it has been found that large slabs cannot be used, because customers require small coil orders from the hot strip mill. At present, this necessitates the use of small slabs in order to fill a small order.

Large slabs could be processed by the hot strip mill if an additional shear was provided at the end of the finish mill to cut the long strips into the desired lengths. However, it may be understood that the use of an additional set of shears would require a mechanical shear, an additional motor and control circuitry; these components are expensive and would add a significant cost to the assembly of the steel mill.

It is therefore an object of this invention to provide new and improved method and control apparatus for cutting strips being processed by a steel mill to provide multiple coils from a single slab.

It is a more particular object of this invention to provide new and improved method and control apparatus for operating the crop shear of 'a steel mill normally used to finish the tail and head ends of the strip, to cut the Patented Nov. 10, 1970 strip into desired lengths to thereby eliminate the need of a second shear at the end of the finishing mill.

SUMMARY OF THE INVENTION These and other objects are accomplished in accordance with the teachings of the present invention by providing a new and improved method and control system for rolling a material such as steel in which the crop shear of a hot strip steel mill is used to cut measured lengths of the strip. More specifically, a length of strip is measured from the head end of the strip, and the crop shear is actuated to cut the desired length of the strip. Illustratively, the leading edge of the strip is sensed by a suitable detector which in turn actuates a length measuring device. As the strip passes, the measuring device will provide a signal indicative of the length of the strip that has passed. Illustratively, the signal could be applied to a computer into which has been fed data con cerning the slab and the desired length of each individual coil to be produced. When the desired length of the strip has passed, the computer will initiate the crop shear to cut the strip.

DESCRIPTION OF THE DRAWINGS These and other objects and advantages of the present invention become more apparent when considered in view of the following detailed description and drawing, which shows a schematic diagram of a hot strip mill arranged and operated in accordance with the teachings of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawing, there is shown an illustrative embodiment of a hot strip mill 10 for successively reducing the thickness of a slab to form an extended workpiece or strip 46. The plurality of slabs are heated in preparation to being rolled in a plurality of furnaces 12. The slabs are extracted from the furnaces 12 and then disposed upon a plurality of tables 14. The tables, in turn, feed the slabs one at a time into a roughing mill 16.

The roughing mill 16 includes a plurality of tables 15 disposed between a plurality of stands RS-l to RS-6 through which the slab is transported for gage reduction.

A greater or fewer number of rolling stands can be provided in the roughing mill 16 if desired. Illustratively,

the first roughing stands to operate upon the strip 46 may I be two high mills including work rolls 19, whereas the later mill stands to operate upon the strip 46'rnay be a four high stand including back-up rolls 20 for pressing the work rolls 19 against the strip 46.

A delay table 22 is disposed between the roughing mill 16 and a finishing mill 26 in order to allow the roughing mill 16 and the finishing mill 26 to be operated independently of each other. The delay table 22 is of such a length to receive the entire strip 46. After the trailing edge of the strip 46 has been rolled onto the delay table 22, the strip 46 may then be fed into the finishing mill 26. The ness of the strip 46. A greater or fewer number of rolling stands FS-l to FS7 for successively reducing the thickness of the strip 46. A greater or fewer number ofrolling stands may be provided in the finishing mill 26. At each stand location, a pair of work rolls 32 and a pair of back-up rolls 34 are provided in a conventional manner. Respective motor drives M1 to M7 are provided at each stand location to drive the work rolls 32 and to transport the strip 46 through the finishing mill 26. A gage reduction produced by the various work rolls 32 is set by controlling the size of the respective work roll openings by the application of the well known roll force principle. 11- lustratively, the drive motors M1 to M7 may take the form of suitably rated DC motors. Regulated power controlled by associated regulators may be applied to the motors M1 to M7 to provide speed and acceleration control of the rollers 32 and thus the strip 46. A crop shear 28 is disposed on the entry side of the finishing mill 26 and a coiler 54 is disposed on the finishing side to receive and to take up the strip 46. The crop shear 28 is of a well known design using two drums 29 each with a blade 27. One drum 29 is disposed under the strip 46 and the other drum is disposed above the strip 46.

The crop shears 28 may serve a dual function: first, the crop shears 28 may operate to trim the leading and trailing edges of the strip 46 so that the strip 46 will thread properly in the finishing mill and will not damage the work rolls 32. With regard to this function, a suitable detector 44- such as heat temperature sensor(s) may be disposed in front of the crop shears 28 to successively detect the leading and trailing ends of the strip 46. Particular reference is made to US. Pat. Nos. 3,082,368 and 3,189,812, assigned to the assignee of the invention, which described a digital control system including two position sensing devices and suitable control circuitry for actuating the crop shears 28 to remove the leading and trailing ends of the strip 46. In a second, analog method, the crop shear control circuit 60 is used to control the rotation of the drums 29. A measuring roll 36 is disposed between the crop shear 28 and the first stand FS1 tomeasure the velocity of the strip 46. Illustratively, the roll 36 may take the form of the pinch roll of a descale unit. The measuring roll 36 is mechanically connected to a suitable speed detector 37 such as a tachometer, which applies a signal indicative of the velocity of the strip 46 to the crop shear control circuit 60. The control circuit 60 illustratively includes a function generator for providing a shaped curve indicative of the delay required before the crop shear 28 is rotated to cut the tail end of the strip 46. The position detector 40 is also connected to the control circuit 60 to indicate the passing of the head and tail ends of the strip 46. The detector 44 may be capable to detect the width of the strip 46 to more accurately determine the cut initiate point on the strip 46. When the trailing edge of the strip 46 passes the detector 44, the function generator initiates the delay curve which is applied to an integrator. It is understood that the integrator is a part of the control circuit 60. The integrator of the circuit 60 measures the delay curve and when a certain value is reached dependent upon the speed of the strip 46, the motor 30 begins to rotate the crop shear drums 29 to cut the strip 46. In order to cut the leading edge of the strip 46, a second measuring roll (not shown) may be disposed in front of the crop shear 28 to apply a signal indicative of the strip velocity to the control circuit 60. After an appropriate delay dependent upon the speed of the strip 46, the crop shear 28 is actuated to cut the head of the strip 46. The second roller may be eliminated if the speed of the strip 46 can be accurately controlled upon the table 22.

In accordance with the teachings of this invention and as shown in the drawing, a control system is provided for actuating the crop shear 28 to cut a specified length of the strip 46. The crop shear 26 is driven by a drive motor 30 which is connected by suitable gearing to the crop shear 28. The crop shear drums 29 are rotated in opposite directions to bring the blades 27 into contact with the strip 46 synchronously in order to cut the strip 46. Further, a load cell 24 is associated with the back up roll 34 of the finishing stand FS-l to detect the roll force applied to the strip 46. The increase in the force due to the entry of the strip 46 and thus the entry of strip 46 into the stand FS-l is detected by the load cell 24.

The overall mill control preferably is provided by a process computer system 58 suitably designed and programmed to provide the degree of process control desired. That portion of the operation of the computer system 58 related to the measurement of the strip 46 and to the 41 control of the crop shear 23 will be explained in particular. A suitable data input device 72 such as a commercially available card reader provides data relating to the length of the strip 46 that is being processed by the finishing mill 26. The computer system 58 has a storage facility for retaining the dimensions of the strip 46 which are of particular interest- In addition, a length control circuit 76 may provide an input to the computer system 58 to place upon the storage facility the desired length of the strip 46 that is to be cut by the crop shear 28. It is noted that in the alternative, this information may be supplied to the computer system 58 by the data input 72.

The computer system 58 will provide an initiating signal to a crop shear control circuit 60 to cause the crop shear drums 29 to be rotated in synchronism to cut the strip 46. The crop shear control circuit 60 in turn supplies a signal to control the output of a power supply 62. The power supply 62 applies a drive signal to the motor 30 for driving the crop shear 28. Illustratively, the motor 30 may be a DC motor whose velocity and position are dependent upon the voltage applied thereto by the power supply 62. The crop shear control circuit 60 functions to control the position of the crop shear drums 29 and to assure that the crop shear drums 29 are in their correct position to cut the strip 46 upon the command of the computer system 58. Further, a suitable position detector 40 such as a shaft encoder is connected to the crop shear 28 in order to provide a feedback signal to the crop shear control circuit 60 indicative of the position of the crop shear drums 29. The crop shear control circuit 60 is responsive to the position detector 40 to thereby accurately control the motor 36. In a similar manner, a suitable speed detector 42 such as a tachometer is associated with the motor 30 to apply a feedback signal to the circuit 60 to accurately control the speed of the motor 30.

As explained above, the load cell 24 functions to detect the entry of the leading edge of the strip 46. A suitable signal is applied from the load cell 24 to a counter initiating circuit 68. Illustratively, the counter initiating circuit 68 applies a signal to the computer system 58. A pulse generator 64 is mechanically connected to the measuring roll 36 disposed between the crop shear 28 and the first finishing stand FS-l. It may be understood that as the strip 46 is driven through the finished mill 26 by the work roll 32 of the finishing stand FS-l that the pulse generator 64 will provide a series of pulses the number of which is indicative of the length of the strip 46 being driven past the roll 36. In turn, the signal provided by the pulse generator 64 is applied to a pulse counter 66, which measures the number of pulses applied thereto. The number of pulses provided by the generator 64 is indicative of the total length of the strip 46 that has passed the roll 36. The pulse counter 66 in turn applies a signal indicative of the current length of the strip 46 to the computer system 58. The computer system 58 compares the signal derived from the length control 70 indicative of the desired length of the strip 46 and the measured length as derived from the pulse counter 66, to initiate the activation of the crop shear 28. It is noted that the measuring of the strip 46 begins when the head of the strip 46 enters the first stand FS-l. The computer system 58 (or counter 66) effectively oifsets a distance equivalent to the distance between the first stand FS1 and the cut initiate point as sensed by the detector 44. When the desired length of strip 46 has been fed into the finished mill 26, the computer 58 will initiate a control signal which is applied to the crop shear control circuit 60. The circuit 60 regulates the driving signal to the motor 30, which, in turn, rotates the crop shear drums 29 to cut the strip 46. In addition, the computer system 58 must energize the shear control circuit 60 a predetermined time before the desired act of cutting by the crop shears 28 in order to allow the motor 30 to drive the crop shear 28 into the cutting position. After the first strip has been run through the finishing mill 26, a second strip will be fed into the mill 26 causing the load cell 24 to apply an appropriate signal to the counter initiating circuit 68. The counter initiating circuit 68 indicates to the computer system 58 that a new strip is being fed into the mill 26. In turn, the computer system 58 resets the pulse counter 66 to start a new counting step to measure the length of the new strip. It is further noted that the counter initiating circuit 68 could apply a reset directly to the pulse generator 64 in order that the next strip 46 may be cut in accordance with the teachings of this invention.

Thus, there has been shown the method and system for controlling a crop shear to serve the dual function of cropping the leading and trailing edges of the strip and further, in accordance with the teachings of this invention, to cut the strip into desired lengths. This invention allows the use of very large slabs, which may be more efliciently processed by the hot strip mill and then cut into desired lengths to fill smaller orders. In addition, this invention avoids the use of a second, expensive shear to be placed at the exit side of the finishing mill.

Since numerous changes may be made in the above described apparatus and difierent embodiments of the invention may be made without departing from the spirit thereof, it is intended that all matter contained in the foregoing description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. A control system for a mill for shearing slabs of material prior to the rolling operation comprising first means for cutting said slab, second means for measuring said slab and providing a first signal indicative of the length of said slab which has passed a reference position, and control means, including a storage facility for retaining the overall length of said slab and the desired length of said slab to be cut, said control means being responsive to said first signal to activate said first means to cut said slab when said desired length has passed said reference position.

2. A control system for a rolling mill as claimed in claim 1, wherein said second means includes third means for detecting the leading edge of said slab and fourth means for measuring the length of said slab passing said point.

3. A control system for a rolling mill as claimed in claim 2, wherein said fourth means includes a circuit for generating pulses which are a function of the length of said slab passing said reference position, and a pulse counting circuit connected with said pulse generating circuit for indicating the length of said slab passing said reference position.

4. A control system for a rolling mill as claimed in claim 3, wherein said third means is coupled to said pulse counting circuit to reset said pulse counting circuit to initiate the measuring the length of a new slab.

5. A method of operating a rolling mill comprising the steps of heating and delivering a workpiece to said mill, measuring a desired length of said workpiece and then cutting said workpiece in at least two strips, further reducing the thickness of said workpiece, and successively coiling said strips into at least two rolls.

6. A method of operating a rollingv mill as claimed in claim 5, wherein the step of measuring is performed by first detecting the leading edge of said strip, then measuring said strip and providing a first signal which is a function of the length of said strip passing a predetermined reference location, and integrating said signal to provide a second signal indicative of the total length of said strip passing said reference location.

References Cited UNITED STATES PATENTS 1,104,349 7/ 1914 Edwards 7214 1,949,717 3/1934 Iversen 7214 2,360,995 10/ 1944 Whitten 729 2,958,243 11/ 1960 Foster 72203 X 3,020,788 2/ 1962 Peters 7212 3,174,316 3/1965 Sigal 72203 X 3,215,015 11/1965 Neely 83-369 X 3,251,212 5/1966 Morgan 72203 3,415,149 12/1968 Ziljberman et a1. 83369 X MILTON S. MEHR, Primary Examiner Us. c1. X.R. 

